optionMONSTER's Depth Charge system shows that 6,391 August 17 puts changed hands throughout the session in a strong buying pattern against open interest of 1,890 contracts. The puts went for prices ranging from $0.08 to $0.15.

Annaly closed yesterday at $17.89, down 1.16 percent on the session. The real-estate investment trust, which pays a dividend yield of about 14 percent, has been trading mostly sideways for the last two years.

The puts could have been bought for protection on a long position or as a straight bet that Annaly would fall in the next month. Either way, they will turn a profit if the stock falls roughly $1 by expiration on Aug. 19.

There was also put buying at the July 18 and October 17 strikes but below open interest, so they could have been closing positions. Overall puts in the name outnumbered calls by more than 2 to 1.